I feel like this has to have been asked and answered 1000 times already, but when I searched I could not find any answer links that matched my question. There seem to be so many variables in adjusting down to a molecular level what gets shown and what gets suppressed by customizing Firefox CSS, or by using about:config . But at this point for me, I am really looking for a DEFAULT USAGE solution. I'm sure there is one and I just don't know it. All I want is to be able to use and '''click Mac's built in UI "Green" button''' in the traffic-light UI element at the top-left corner of a window, and have the browser obey and: strip out or suppress all Firefox browser "chrome" elements such as tab bar, URL bar, bookmarks bar -- and show me the webpage I am looking at truly full-screen. Then when done with full-screen view, I want to click/toggle Mac's "green light" button again and have all the Firefox browser UI elements return. (Tab bar, URL bar, bookmarks bar).